1. Field
The present disclosure relates generally to communications and, in particular, to controlling the transmission of information on a carrier signal. Still more particularly, the present disclosure relates to a method and apparatus for producing a transmission of constant envelope on a carrier signal.
2. Background
In the field of communications, information is sometimes sent via a carrier signal. The carrier signal is a type of signal having a shape and form that is modulated to encode the information into the signal for transmission. The carrier signal has a tonal frequency known as the carrier tone. The carrier tone is not modified when information is modulated onto the carrier signal. For example, a carrier signal can be used to send information over the air or through space as an electromagnetic wave.
Today, most information sent over a carrier signal is digital information. This digital information is typically received as a sequence of bits for transmission by the carrier signal. If the information to be sent over the carrier signal is from an analog signal, the analog signal is first converted into digital information for transmission over the carrier signal. Each of the bits has a value of +1 or −1.
The information sent on a carrier signal may come from many sources. Even when the information is from one source, multiple sequences of bits of information may be sent at the same time over the carrier signal. Before a sequence of bits of information is modulated onto the carrier signal, the sequence of bits is typically first spread using a component code selected for the sequence of bits. When multiple spread sequences of bits are transmitted via a single carrier signal, a signal combining technique is typically used to combine the spread sequences of bits into a composite sequence of bits before transmission.
These component codes are sequences of chips. The chips typically have values of +1 or −1. The term “chips” was chosen to reduce confusion with the term bits used in the sequence of bits of information.
When the carrier tone of the carrier signal is modulated to transmit a composite sequence of bits of information, power efficiency of the carrier signal can be reduced. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. For example, it would be desirable to have a method and apparatus that increase power efficiency of a carrier Lone of a carrier signal when the carrier tone is modulated to transmit a composite sequence of bits of information.